Operation K

At about two in the morning on 4 March 1942 the people of Honolulu were woken by explosions. Four bombs fell on the wooded slopes of Tantalus, an extinct volcano above the city, a few hundred metres from Roosevelt High School. They broke windows in nearby houses but killed and injured no one. They had been dropped by one of two Japanese flying boats that had flown thousands of kilometres from the Marshall Islands, refuelling on the way from submarines at an uninhabited atoll. Their task was to photograph and bomb the fleet base at Pearl Harbor (PL). The Japanese called the mission Operation K. Militarily it achieved nothing, but it was one of the longest bombing missions flown up to that time.

The plan

After the attack on Pearl Harbor the Japanese navy wanted to know how quickly the Americans were repairing the damage. Reconnaissance aircraft launched from submarines off Hawaii flew over twice, on 17 December 1941 and 5 January 1942, and found frantic repair work under way at the base. Further reconnaissance, however, called for an aircraft that could reach Hawaii from the nearest Japanese bases in the Marshall Islands, more than 3,500 kilometres away.

That aircraft was to be the new Kawanishi H8K flying boat, later codenamed “Emily” by the Americans – a four-engined machine of exceptional range that had only just entered service. The Naval General Staff and the staff of Admiral Isoroku Yamamoto’s Combined Fleet concluded that it could combine reconnaissance with a raid. In the second half of January the Combined Fleet’s chief of staff, Rear Admiral Matome Ugaki, instructed the commands of Vice Admiral Shigeyoshi Inoue’s Fourth Fleet and of the Sixth Fleet, which grouped the submarines, to prepare the operation.

The plan was a bold one. The flying boats were to take off from Wotje atoll and, after a flight of more than ten hours, alight in the lagoon of French Frigate Shoals, an uninhabited atoll in the chain of the Northwestern Hawaiian Islands. Submarines waiting there, adapted to carry aviation fuel, would refuel them. From there it was only about 900 kilometres to Oʻahu. The main target was the 1,010-foot (about 310-metre) repair wharf at Pearl Harbor, known as “Ten-Ten”, where the ships damaged on 7 December were being repaired. The attack was meant to hamper the work, bring back photographs of the state of the base and show the Americans that their main base in the Pacific still lay within reach of Japanese bombs. The raid was timed for the full moon; if it succeeded, others were to follow.

The original intention was to use five H8Ks, but only two prototype aircraft were ready for action. The mission was led by Lieutenant Hisao Hashizume; the second aircraft was flown by Ensign Shōsuke Sasao. In mid-February the two flying boats flew via Saipan and Truk to Jaluit atoll. The operation was delayed by American carrier raids – the strike on the Marshall and Gilbert Islands on 1 February was followed by an attempted strike on Rabaul (20 February) and a raid on Wake (24 February), and the submarines earmarked for the operation had to hunt for the carriers. In the end the submarines I-15 and I-19 sailed for French Frigate Shoals, with a third in reserve; I-9 took station on the route as a radio beacon, and I-23 was to wait south of Oʻahu to report the weather and rescue aircrews. The latter, however, disappeared in the second half of February from unknown causes.

The flight

On 2 March the flying boats moved to Wotje, where each took on four 250-kilogram bombs. They took off just after midnight on 4 March Tokyo time (in Hawaii, on the other side of the International Date Line, it was still the morning of 3 March), alighted at French Frigate Shoals at dusk, refuelled from I-15 and I-19 and after dark flew on over Necker Island, Niʻihau and Kauaʻi.

The Americans had some warning. Fleet radio intelligence at Pearl Harbor had read in Japanese signals traffic that the navy was preparing reconnaissance and harassing flights with refuelling at French Frigate Shoals. The fleet intelligence officer, Edwin Layton, had on his staff Lieutenant Jasper Holmes, who in 1941 had published under a pen name a story in The Saturday Evening Post about aircraft refuelled from a submarine at a remote islet before a raid on a target thousands of miles away. According to American accounts, however, the warnings were not taken very seriously. When a radar station on Kauaʻi detected approaching aircraft shortly after midnight, they were at first taken to be friendly. Later an air-raid alert was sounded, P-40 fighters were scrambled and Catalinas were sent out to search for the Japanese carriers from which, it was assumed, the intruders must have come.

A thick layer of cloud lay over Oʻahu. It saved the flying boats from the fighters, which failed to find them, but it also robbed the Japanese of their target. The island was blacked out. Hashizume fixed his position by the lighthouse at Kaʻena Point and decided to attack from the north; Sasao did not hear the order and turned along the south coast. Hashizume, seeing only scraps of land through gaps in the cloud, dropped his bombs on the slopes of Tantalus. Sasao’s bombs most probably fell into the sea, off the island’s west coast or near the entrance to Pearl Harbor. The craters were up to three metres deep and up to nine across. No photographs of the base were taken.

Both aircraft returned to the Marshall Islands on the morning of 5 March Japanese time. One of them had damaged its hull bottom taking off from the lagoon at French Frigate Shoals and, instead of Wotje, flew non-stop to Jaluit. According to most accounts this was Hashizume’s aircraft, which made his flight the longest bombing mission in history up to that day.

Consequences

There was no damage, but the raid alarmed Hawaii, which had lived in fear of invasion since December. Since nobody had seen any aircraft over the city, the army and the navy accused each other of having had one of their units jettison ammunition over Tantalus. The Japanese press, for its part, repeated unconfirmed reports from American radio in Los Angeles of “considerable damage” at Pearl Harbor, with thirty killed and seventy wounded. In those same days the US west coast was still reverberating with the shelling of an oil refinery near Santa Barbara by a Japanese submarine (23 February) and the night-time “Battle of Los Angeles” of 25 February.

The second raid, planned for 6–7 March, never took place: the damaged aircraft needed about ten days of repairs, the crews were exhausted, and the phases of the moon and conditions at sea did not allow any waiting. Instead the Combined Fleet ordered reconnaissance of Midway and Johnston Atoll. On 10 March radar at Midway picked up Hashizume’s aircraft; Marine fighters – Brewster Buffalos, according to American sources – shot it down, and the whole crew was killed.

The most important consequences, however, came three months later. As Yamamoto prepared the operation against Midway, the Combined Fleet staff wanted to check before the battle whether the American carriers were at Pearl Harbor. This was to be done by repeating Operation K, again with refuelling at French Frigate Shoals. The Americans, meanwhile, had worked out from radio traffic that the Japanese had used the atoll as a staging point, and Admiral Chester Nimitz had it guarded. When the submarine I-123 approached the atoll on 30 May 1942, it found the minelayer USS Preble and the seaplane tender USS Thornton in the lagoon; some studies say the Americans had also mined the area beforehand. I-121 arrived the next day, but the American ships did not leave, and on 1 June the second Operation K was called off.

The Japanese thus lost their only chance to look into Pearl Harbor before the battle. They did not know that Enterprise, Hornet and the hastily repaired Yorktown had already sailed and were waiting north-east of Midway. The submarine screen that was supposed to detect them in transit also took up its positions too late. The Combined Fleet command accepted the cancellation of the flight without concern, convinced that the American fleet would leave Hawaii only after the attack on the atoll. In the Battle of Midway at the beginning of June 1942 American aircraft sank four Japanese carriers. The failed night raid of 4 March, which left only a few craters on a hillside above Honolulu, thus contributed indirectly to the Americans being able to strike there by surprise.